When I put my gyt twins on last year i kept the 153.8 mains, dropped the needles one clip and didn't change to the Q8 needles. I have not put a ton of miles on it but my plugs look good as does my wash, both are a little on the rich side. Im around 1800ft above sea level. I feel my jetting is good till about -15 to -18, ran it in that yesterday on the river and it absolutely ripped. It does move your powerband up 1200 or so rpm though, and it LOVES its fuel now even moreso than before if you can imagine that. If you do a search there is a ton of info about this subject. I know my setup is not perfect but it works good enough for me.